1. Field of the Invention
The present invention relates to a composition, a film using the composition, a charge transport layer, an organic electroluminescence device, and a method for forming a charge transport layer. The composition of the invention is useful as a composition for organic electroluminescence device.
2. Description of the Related Art
With respect to devices utilizing an organic material, studies regarding an organic electroluminescence device (hereinafter sometimes as “OLED” or “organic EL device”), a transistor utilizing an organic semiconductor, and the like are actively carried out. In particular, organic electroluminescence devices are expected to be developed for large-area full-color display devices of a solid emission type or illumination applications as an inexpensive large-area surface light source. In general, an organic electroluminescence device is constituted of an organic layer including a light emitting layer and a pair of counter electrodes interposing the organic layer therebetween. When a voltage is impressed to such an organic electroluminescence device, an electron is injected from a cathode, and a hole is injected from an anode, respectively into the organic layer. The electron and the hole are recombined in the light emitting layer, and at the time when an energy level returns from a conduction band to a valence band, energy is released as light, thereby obtaining light emission.
An organic EL device can be fabricated by film-forming a light emitting layer and other organic layer by means of, for example, a dry method such as vapor deposition or a wet method such as coating. Above all, a wet method is given attention from the viewpoint of productivity or the like.
It is known that in an organic EL device fabricated by means of a wet method such as coating, when an arylamine derivative having a polymerizable group (for example, a vinyl group or an allyl group) is used as a hole transport layer forming material, light emission efficiency of the organic EL device increases, and durability is enhanced.
In the related art, it is known that when an arylamine derivative having a polymerizable group is film-formed with a polymerization initiator-free coating liquid, and the polymerizable group is polymerized in an inert gas (N2) atmosphere by heating or upon irradiation with ultraviolet light (UV light) to crosslink the arylamine derivative, thereby forming a layer, the layer is insolubilized in the coating liquid for forming a light emitting layer. For example, JP-A-2008-4671 discloses that a coating solution having an arylamine derivative having a polymerizable group dissolved in toluene is coated, irradiated with ultraviolet light (UV light) for 30 seconds and then dried in vacuo at 60° C. for one hour, thereby forming a hole transport layer. Also, JP-A-2009-16739 discloses that a solution of an arylamine derivative having an acryloyl group as a polymerizable group dissolved in methyl isobutyl ketone is coated and then heated for curing at 200° C. for 30 minutes, thereby forming a hole injection layer.
However, when ultraviolet light is irradiated, there may be the case where a decomposition reaction of the arylamine derivative is caused due to the ultraviolet light, and there is a concern that desired characteristics to be caused due to the arylamine derivative are lost. In consequence, it is demanded to allow a polymerization reaction to proceed with efficiency without irradiation with ultraviolet light.
Also, in order to form a film capable of providing suitable device characteristics by means of a polymerization reaction by only heating, since a high-temperature and long-term polymerization reaction is required, it is demanded to improve a manufacturing condition. Specifically, it is demanded that not only the polymerization reaction proceeds with efficiency at a milder temperature and for a short period of time, but an organic EL device using a film formed therefrom has favorable device characteristics.